1. Field of the Invention
This invention relates to rubber compositions having improved stability in initial tack with reduced dependence on temperature prior to curing.
2. Description of the Prior Art
Various rubber compositions are known for use in applying or coating reinforcement cords of nonmetallic or metallic origin adapted to be assembled in pneumatic automobile tires and conveyor belts. These compositions before being subject to curing are rather dependent on temperature and necessarily variable or irregular in tackiness at ambient temperature. This tendency is markedly seen where organic cobalt compounds are blended to improve adhesion of rubbers to steel cords. In such instance objectionably excessive tack will develop with temperature rises in the hot season. With the reinforcing cords obtained by coating with the above prior compositions, the resulting rubbery sheets will become too tacky to be handled and cause those tires and belts to be produced at a low rate.
Attempts have been made to reduce tackiness with use of paraffin waxes chosen to meet seasonal changes or varying temperatures. To this end those waxes for use in the hot season have a maximum peak in the carbon area in the vicinity of 34 carbon atoms and those for use in the cold season at around 27 carbon atoms. Such carbon areas are determined with resort to a graphical chart in which the total carbon area of paraffin waxes within a predetermined number of carbon atoms is counted by means of gas chromatography and thereafter plotted against the carbon number. A distribution curve of carbon number to carbon area is thus drawn for quick reference from which either one paraffin wax is selected to provide a good balance between the tack quality and the ambient temperature.
The above mode of wax selectivity, however, is wholly unsatisfactory as the ultimate composition when held not constant at ambient temperature is encountered with insufficient tackiness and oftentimes with instable initial tack owing to irregular wax blooming. An impetus therefore has been given to the advent of rubber compositions free from the foregoing drawbacks of the prior art.